Nonlinear spectroscopy based on parametric down-conversion of X-rays into ultra-violet radiation

Speaker:  Sason Sofer

Program Description:

Nonlinear interactions between x-rays and long wavelengths can be used as a

powerful atomic scale probe for light-matter interactions and for properties of valence

electrons. This probe can provide novel microscopic information in solids that existing

methods cannot reveal, hence, to advance the understanding of many phenomena in

condensed matter physics. However, thus far, reported x-ray nonlinear effects were very

small and their observations required tremendous efforts. In this talk, I will present the observation

of unexpected strong nonlinearities in parametric down-conversion (PDC) of x-rays to long

wavelengths in gallium arsenide (GaAs) and in lithium niobate (LiNbO3 ) crystals, with

efficiencies that are about 4 orders of magnitude stronger than the efficiencies measured

in any material studied before. These strong nonlinearities cannot be explained by any

known theory and indicate on possibilities for the development of a new spectroscopy

method that is orbital and band selective. In this work we demonstrate the ability to use

PDC of x-rays to investigate the spectral response of materials in a very broad range of

wavelengths from the infrared regime to the soft x-ray regime.